[hvdijk]

Even for those that do not assume GNU make, this may not be enough. GNU Autotools are not limited to running on GNU make, but this make does not implement everything used by Autotools. The first thing I noticed it does not handle is VPATH (https://www.gnu.org/software/make/manual/html_node/General-S...) which is used by Autotools for out-of-tree builds (mkdir build && cd build && ../configure && make as opposed to ./configure && make).

[zxwrt]

But out-of-tree builds feature is optional, right?

[hvdijk]

It depends on the package. As far as Autotools itself are concerned, yes, users are free to choose whether to do in-tree or out-of-tree builds, but some packages require one or the other.